The brother of a man accused of organising the suicide bombing on the St Petersburg subway has been arrested, Russia's Federal Security Service says.
The security service, known as the FSB, said it arrested Akram Azimov in a town near Moscow on Wednesday.
He is being held on suspicion of providing money to his younger brother Abror to prepare for the April 3 subway bombing and of aiding him in contacts with unspecified terrorist organisations.
Abror Azimov was arrested on Monday and charged with organising the attack that killed 14 passengers.
The FSB said he is believed to have helped prepare the suicide bomber.
There has been no claim of responsibility for the attack, but the suicide bomber is alleged to have had ties to Islamic extremists.